The present invention relates to semiconductor thin film processing. The fabrication of modern semiconductor device structures has traditionally relied on plasma processing in a variety of operations such as etching and deposition. Plasma etching involves using chemically active atoms or energetic ions to remove material from a substrate. Deposition techniques employing plasma includes Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) or sputtering. PVD uses a high vacuum apparatus and generated plasma that sputters atoms or clusters of atoms toward the surface of the wafer substrates. PVD is a line of sight deposition process that is more difficult to achieve conform film deposition over complex topography such as deposition of a thin and uniform liner or barrier layer over the small trench or via of 0.13 xcexcm or less, especially with high aspect ratio greater than 4:1.
In CVD, a gas or vapor mixture is flowed over the wafer surface at an elevated temperature. Reactions then take place at the hot surface where deposition takes place. Temperature of the wafer surface is an important factor in CVD deposition, as it depends on the chemistry of the precursor for deposition and affects the uniformity of deposition over the large wafer surface. CVD typically requires high temperature for deposition which may not be compatible with other processes in the semiconductor process. CVD at lower temperature tends to produce low quality films in term of uniformity and impurities. More details on PVD and CVD are discussed in International Pub. Number WO 00/79019 A1 or PCT/US00/17202 to Gadgil, the content of which is incorporated by reference.
In a deposition technology known as atomic layer deposition (ALD), various gases are injected into the chamber for as short as 100-500 milliseconds in alternating sequences. For example, a first gas is delivered into the chamber for about 500 milliseconds and the substrate is heated, then the first gas (heat optional) is turned off. Another gas is delivered into the chamber for another 500 milliseconds (heat optional) before the gas is turned off. The next gas is delivered for about 500 milliseconds (and optionally heated) before it is turned off. This sequence is done for until all gases have been cycled through the chamber, each gas sequence forming a monolayer which is highly conformal. ALD technology thus pulses gas injection and heating sequences that are between 100 and 500 milliseconds. This approach has a high dissociation energy requirement to break the bonds in the various precursor gases such as silane and oxygen and thus requires the substrate to be heated to a high temperature, for example in the order of 600-800 degree Celsius for silane and oxygen processes.
U.S. Pat. No. 5,916,365 to Sherman entitled xe2x80x9cSequential chemical vapor depositionxe2x80x9d provides for sequential chemical vapor deposition by employing a reactor operated at low pressure, a pump to remove excess reactants, and a line to introduce gas into the reactor through a valve. Sherman exposes the part to a gaseous first reactant, including a non-semiconductor element of the thin film to be formed, wherein the first reactant adsorbs on the part. The Sherman process produces sub-monolayers due to adsorption. The first reactant forms a monolayer on the part to be coated (after multiple cycles), while the second reactant passes through a radical generator which partially decomposes or activates the second reactant into a gaseous radical before it impinges on the monolayer. This second reactant does not necessarily form a monolayer but is available to react with the monolayer. A pump removes the excess second reactant and reaction products completing the process cycle. The process cycle can be repeated to grow the desired thickness of film.
U.S. Pat. No. 6,200,893 to Sneh entitled xe2x80x9cRadical-assisted sequential CVDxe2x80x9d discusses a method for CVD deposition on a substrate wherein radical species are used in alternate steps to depositions from a molecular precursor to treat the material deposited from the molecular precursor and to prepare the substrate surface with a reactive chemical in preparation for the next molecular precursor step. By repetitive cycles a composite integrated film is produced. In a preferred embodiment the depositions from the molecular precursor are metals, and the radicals in the alternate steps are used to remove ligands left from the metal precursor reactions, and to oxidize or nitride the metal surface in subsequent layers.
In one embodiment taught by Sneh, a metal is deposited on a substrate surface in a deposition chamber by (a) depositing a monolayer of metal on the substrate surface by flowing a molecular precursor gas or vapor bearing the metal over a surface of the substrate, the surface saturated by a first reactive species with which the precursor will react by depositing the metal and forming reaction product, leaving a metal surface covered with ligands from the metal precursor and therefore not further reactive with the precursor; (b) terminating flow of the precursor gas or vapor; (c) purging the precursor with inert gas; (d) flowing at least one radical species into the chamber and over the surface, the radical species highly reactive with the surface ligands of the metal precursor layer and eliminating the ligands as reaction product, and also saturating the surface, providing the first reactive species; and (e) repeating the steps in order until a metallic film of desired thickness results.
In another Sneh aspect, a metal nitride is deposited on a substrate surface in a deposition chamber by (a) depositing a monolayer of metal on the substrate surface by flowing a metal precursor gas or vapor bearing the metal over a surface of the substrate, the surface saturated by a first reactive species with which the precursor will react by depositing the metal and forming reaction product, leaving a metal surface covered with ligands from the metal precursor and therefore not further reactive with the precursor; (b) terminating flow of the precursor gas or vapor; (c) purging the precursor with inert gas; (d) flowing a first radical species into the chamber and over the surface, the atomic species highly reactive with the surface ligands of the metal precursor layer and eliminating the ligands as reaction product and also saturating the surface; (e) flowing radical nitrogen into the chamber to combine with the metal monolayer deposited in step (a), forming a nitride of the metal; (f) flowing a third radical species into the chamber terminating the surface with the first reactive species in preparation for a next metal deposition step; and (g) repeating the steps in order until a composite film of desired thickness results.
The Sneh embodiments thus deposit monolayers, one at a time. This process is relatively time-consuming as a thick film is desired.
In comparison with CVD, atomic layer deposition (ALD or ALCVD) is a modified CVD process that is temperature sensitive and flux independent. ALD is based on self-limiting surface reaction. ALD provides a uniform deposition over complex topography and temperature independent since the gases are adsorbed onto the surface and lower temperature than CVD because it is in adsorption regime.
As discussed in Sherman and Sneh, the ALD process includes cycles of flowing gas reactant into the chamber, adsorbing one sub-monolayer onto the wafer surface, purging the gas reactant, flowing a second gas reactant into the chamber, and reacting the second gas reactant with the first gas reactant to form a monolayer on the wafer substrate. Thick film is achieved by deposition of multiple cycles.
Precise thickness can be controlled by number of cycles since monolayer is deposited per cycle. However, the conventional ALD method is slow in depositing films such as those around 100 angstroms in thickness. Growth rate of ALE TiN for example was reported at 0.2 angstrom/cycle, which is typical of metal nitrides from corresponding chlorides and NH3.
The throughput in device fabrication for a conventional ALD system is slow. Even if the chamber is designed with minimal volume, the throughput is still slow due to the large number of cycles required to achieve the thickness. Conventional ALD is a slower process than CVD with a rate of deposition almost 10 times as slow as CVD deposition. The process is also chemical dependent to have the proper self-limiting surface reaction for deposition.
In one aspect, a process of depositing a thin film by chemical vapor deposition includes evacuating a chamber of gases; exposing a device to a gaseous first reactant, wherein the first reactant deposits on the device to form the thin film; evacuating the chamber of gases; and exposing the device, coated with the first reactant, to a gaseous second reactant under plasma, wherein the thin film deposited by the first reactant is treated to form the same materials or a different material.
Implementations of the above aspect may include one or more of the following. The device can be a wafer. The plasma enhances or maintains the thin film conformality. The plasma can be a high density plasma with higher than 5xc3x97109 ion/cm3. The reactant can be a metal organic, organic, to form a thin film of metal, metal nitride, or metal oxide. The second reactant is exposed under high pressure above 100 mT. The first and second reactants react and the reaction creates a new compound. The thin film thickness is more than one atomic layer thickness. The thin film thickness can be between a fraction of a nanometer and tens of nanometers. The plasma can be sequentially pulsed for each layer to be deposited. The plasma can be excited with a solid state RF plasma source such as a helical ribbon electrode. The chamber containing the device can be purged. The process includes pre-cleaning a surface of a device; evacuating a chamber; stabilizing precursor flow and pressure; exposing the device to a first reactant, wherein the first reactant deposits on the device to form the nanolayer thin film having a thickness of more than one atomic layer; purging the chamber; evacuating the chamber; striking the plasma; performing a plasma treatment on the deposited film; exposing the device, coated with the first reactant, to a gaseous second reactant under the plasma treatment, wherein the thin film deposited by the first reactant is treated to form the same materials or a different material. Repeating of the nanolayer deposition steps deposit a thick film with thickness controlled by the number of repeats.
In another aspect, the deposition steps discussed above can take place in multiple chambers. The process includes pre-cleaning of the device surface, evacuating the chamber, stabilizing precursor flow and pressure, exposing the device to a first reactant, wherein the first reactant deposits on the device to form the nanolayer thin film having a thickness of more than one atomic layer, purging the chamber, evacuating the chamber; then the device is transferred to another chamber that is purged and pumped, then striking the plasma, performing a plasma treatment on the deposited film, exposing the device, coated with the first reactant in the first chamber, to a gaseous second reactant under the plasma treatment in the second chamber, wherein the thin film deposited by the first reactant is treated to form the same materials or a different material. Repeating of the nanolayer deposition steps between the first and second chambers deposit a thick film with thickness controlled by the number of repeats.
In another aspect, an apparatus to perform semiconductor processing includes a high density inductive coupled plasma generator to generate plasma; and a process chamber housing the plasma generator, wherein the chamber exposes a device to a gaseous first reactant, wherein the first reactant deposits on the device to form the thin film and, after purging, exposes the device, coated with the first reactant, to a gaseous second reactant under plasma, wherein the thin film deposited by the first reactant is treated to form the same materials or a different material. The method can provide deposition of copper metal from Cu hfacI and plasma (gas), Cu hfacII and plasma (gas), CuI4 and plasma (gas), CuCl4 and plasma (gas), and organo metallic and plasma (gas); of titanium nitride from TDMAT and plasma (gas), TDEAT and plasma (gas), TMEAT and plasma (gas), TiCl4 and plasma (gas), Til4 and plasma (gas), and organo metallic and plasma (gas); of tantalum nitride from PDMAT and plasma (gas), PDEAT and plasma (gas), and organo metallic and plasma (gas); wherein gas is one of N2, H2, Ar, He, NH3, and combination thereof.
Implementations of the apparatus can include gas distribution, chuck, vaporizer, pumping port to pump, and port for gas purge.
Advantages of the system may include one or more of the followings. The resulting deposition is highly conformal and is similar in quality to that of atomic layer deposition. The nanolayer thick film deposition process provides almost 100% conformal deposition on complex topography as that in semiconductor devices having 0.1 micron width with an aspect ratio greater than 8:1. Excellent conformality of film is achieved with NLD similar to that of ALD, and far superior than conformality of thick CVD film. Further, such conformality is achieved at high speed since multiple atomic layers are deposited at once, in contrast to conventional monolayer deposition techniques such as atomic layer deposition technique. In each cycle of NLD process, a film with thickness of more than a monolayer to a few nanometers is deposited. The advantage of NLD over ALD is thus throughput is higher than that of ALD, since multiple atomic layers are deposited in contrast to ALD.
The microstructure of the film resulting from NLD can be of a nanocrystalline grain structure in an amorphous matrix using the NLD technique, since a film of more than a monolayer to a few nanometer thick is deposited in each cycle. This structure is not typical of conventional CVD or PVD processes. The surface morphology of the films deposited by NLD technique is also smoother than that of films deposited by the conventional CVD technique. This microstructure and morphology can be ideal for certain applications. In the application of copper diffusion barrier thin film deposition, this microstructure of the barrier thin film is a key to the resistance to copper. In fact, our initial data show that our NLD TiN film deposited from TDMAT precursor and N2 plasma has superior barrier properties to PVD TiN, PVD TaN, or conventional CVD TiN. Additionally, the low temperature of the NLD deposition process (lower than CVD) is consistent with the processing requirements of advanced films such as low-k dielectric.
The precursors or gases in NLD process are not limited to only those having the self-limiting surface reactions since NLD is a deposition process. NLD thus is precursor-dependent and can be used to deposit a vast number of film materials from currently available precursors. Since NLD process has high throughput, the minimal volume constraint as in ALD process is not necessary, and conventional CVD chamber can be used to achieve highly conformal, high quality, high throughput films.
Other advantages of the system may include one or more of the followings. The helical ribbon provides a highly uniform plasma and also results in a chamber with a small volume. The system enables high precision etching, deposition or sputtering performance. This is achieved using the pulse modulation of a radio frequency powered plasma source, which enables a tight control the radical production ratio in plasmas, the ion temperature and the charge accumulation. Also, since the time for accumulation of charges in a wafer is on the order of milli-seconds, the accumulation of charges to the wafer is suppressed by the pulse-modulated plasma on the order of micro-seconds, and this enables the suppression of damage to devices on the wafer caused by the charge accumulation and of notches caused during the electrode etching process. The system requires that the substrate be heated to a relatively low temperature such as 400 degrees Celsius.
Yet other advantages may include one or more of the followings. The system attains highly efficient plasma operation in a compact substrate process module that can attain excellent characteristics for etching, depositing or sputtering of semiconductor wafers as represented by high etch rate, high uniformity, high selectivity, high anisotropy, and low damage. The system achieves high density and highly uniform plasma operation at low pressure for etching substrates and for deposition of films on to substrates. Additionally, the system is capable of operating with a wide variety of gases and combinations of gases, including highly reactive and corrosive gases.